Motivated by a recent proposal that points to the Sombrero galaxy as a source of the highest energy cosmic rays, we investigate the feasibility of accelerating both light and heavy nuclei near the supermassive black hole located at the center of this nearly edge-on galaxy that is just beyond naked-eye visibility. We show that cosmic ray nuclei concentrated in the immediate vicinity of the supermassive black hole could be efficiently accelerated up to the maximum observed energies without suffering catastrophic spallations. Armed with our findings we stand against conventional wisdom and conjecture that accelerators of the highest energy cosmic rays must anticorrelate with the (electromagnetic) source power.

Phenomenological studies of cosmic-ray self-confinement often hinge on the linear theory for the growth rate of the streaming instability and for the damping rate of the generated magnetic modes. Largely different expressions exist, especially for the rate of nonlinear Landau damping, which is often assumed to be the most important damping mechanism in warm ionized plasmas. Using hybrid-particle-in-cell simulations in the resonant streaming instability regime, we present a comprehensive assessment of nonlinear Landau damping and show that the damping rate at a given scale depends on the power in magnetic fields on larger scales. Furthermore, we find that an inverse cascade develops, which produces magnetic fields on scales larger than the resonant ones. Here, we extend previous results obtained for a monoenergetic distribution of nonthermal particles to the case of broader cosmic ray (CR) distributions, as a first step toward developing phenomenological models. Preexisting turbulence of Alfvénic nature at large scales severely affects the damping of waves produced by low-energy CRs; depending on its amplitude, such a turbulence may inhibit the growth of streaming instability so that CRs are either self-confined at all energies or not at all.

We investigate photon, pion, and $\rho$-meson production from proton synchrotron radiation in the presence of strong magnetic fields. The proton decay widths and the luminosities of the emitted particles are calculated within a relativistic quantum framework that incorporates Landau quantization. A scaling rule is derived for the transition probability between different Landau levels. This allows an evaluation of transitions for extremely high Landau numbers exceeding ${10}^{15}$. Furthermore, we calculate the momentum distribution of the emitted particles by properly including the proton recoil effect associated with particle emission. The results differ significantly from conventional semiclassical approaches.

Individual supermassive binary black holes (SMBBHs) are anticipated to be detected by pulsar timing arrays (PTAs) in the nanohertz band. The gravitational waves (GWs) from some of those individual SMBBHs may be diffractionally lensed by intervening galaxies. If on circular orbits, however, it is difficult to identify these lensed SMBBHs only by their GW signals, as their monochromatic waveforms are different from the original unlensed ones only with a small amplitude amplification and phase shift, which can be fit by unlensed waveforms with larger chirp masses or smaller distances. In this paper, we investigate whether we can identify the lensed nanohertz GW signals from highly eccentric SMBBHs by exploiting the dependence of their amplification on the frequencies of different harmonics. We adopt the second post-Newtonian GW waveform from eccentric SMBBHs and the singular isothermal sphere lens model to calculate the difference between the lensed waveforms and the matched filtering ones with unlensed GW templates for different lensed systems, and find the larger the eccentricity, the larger the difference. Assuming the square kilometer array-PTA configuration, we adopt the fitting factor to justify the distinguishability of lensed GW signals from unlensed ones and find that we may identify some of the lensed sources with higher eccentricities ($\gtrsim 0.6$) via 30-yr observations. The identification of diffraction lensed SMBBHs may provide an important probe to the wave nature of GWs and its astrophysical applications.

We tackle the issue of estimating dynamical parameters in quantum electrodynamics. We numerically compute the quantum Fisher information matrix (QFIM) of physical parameters in electron-muon and Compton scattering at tree level. In particular, we consider the estimation of center-of-mass three-momentum magnitude and polar scattering angle through measurements on the internal degrees of freedom (helicity or polarization) of the scattered particles. Computations are carried out for pure and maximally mixed initial states. The QFIM values are then used to compute the quantum Cramér-Rao lower bounds on the estimations at hand. Further, we compare such ultimate bounds to the classical Fisher information of local polarization or helicity degrees of freedom.

In many extensions of the Standard Model electroweak phase transitions at high temperatures can be described in a minimal dimensionally reduced effective theory with SU(2) gauge field and fundamental Higgs scalar. In this effective theory, all thermodynamic information is governed by two dimensionless ratios $x\equiv {\lambda }_3/g_3^2$ and $y\equiv m_3^2/g_3^4$, where ${\lambda }_3$, $m_3^2$, and $g_3$ are the effective thermal scalar self-interaction coupling, the thermal mass and the effective gauge-coupling, respectively. By using nonperturbative lattice simulations to determine the rate of sphaleron transitions in the entire $(x,y)$-plane corresponding to the Higgs phase, and by applying previous lattice results for the bubble nucleation, we find a condition $x(T_c)\lesssim 0.025$ to guarantee preservation of the baryon asymmetry, which translates to $v/T_c\equiv \sqrt{2\mathrm{\Delta }⟨{\varphi }^{†}\varphi ⟩}/T_c\gtrsim 1.33$ for the (gauge-invariant) discontinuity in Higgs condensate. This indicates that viability of the electroweak baryogenesis requires the phase transition to be slightly stronger than previously anticipated. Finally, we present a general template for analysing such viability in a wide class of beyond the Standard Model theories, in which new fields are heavy enough to be integrated out at high temperature.

Van der Waals potentials describing interactions between color-singlet mesons and/or baryons vanish at leading order in potential nonrelativistic quantum chromodynamics (pNRQCD). This result and constraints from Gauss’s law are used to prove that weakly coupled pNRQCD van der Waals potentials in generic non-Abelian gauge theories with only heavy quarks are too weak to form bound states whose color state is a product of color singlets. Quantum Monte Carlo calculations of four, five, and six quarks with equal masses provide numerical evidence that exotic color configurations are higher energy than products of color-singlet hadrons, suggesting that equal-mass fully heavy tetraquark, pentaquark, and hexaquark bound states do not exist at next-to-leading order in pNRQCD and at all orders in QCD-like theories in which all quark masses are asymptotically large. Mechanisms for generating hadron-hadron bound states are identified, which necessarily involve large quark-mass hierarchies, relativistic effects arising from the presence of sufficiently light quarks, or nonperturbative effects outside the scope of weakly coupled pNRQCD.

We compute the coefficients $c_2(T,B)$ and $c_4(T,B)$ of the Taylor expansion for the pressure in powers of ${\mu }_B/T$ in the presence of a large magnetic field within perturbative quantum chromodynamics (QCD) at finite temperature and baryon density up to two-loops for $N_f=3$ flavors with physical quark masses. We also present results for the excess of pressure, baryon density, and baryon number susceptibility as functions of ${\mu }_B$, as well as susceptibilities as functions of the temperature in the $\{{\mu }_B,{\mu }_Q,{\mu }_S\}$ basis. Our results can be directly compared to recent lattice QCD data. Even though current lattice results do not overlap with its region of validity, perturbative results seem to be compatible with those obtained on the lattice for large temperatures.

We study the Columbia plot for the chiral phase transition in the framework of a three-flavor linear sigma model based on the Cornwall-Jackiw-Tomboulis (CJT) formalism. The conventional CJT approach with the Hartree truncation suffers from artificial chiral breaking, leading to the violation of the Nambu-Goldstone theorem and the (anomalous) chiral Ward-Takahashi identities. We apply the symmetry-improved CJT formalism to resolve this issue. We observe a first-order phase transition and a tricritical point in the light-quark mass regime, which is relatively independent of the size of the sigma meson, in contrast to the conventional CJT approach. The tricritical point, found on the $m_s$ axis, is at $m_s^{\mathrm{tri}}/m_s^{\mathrm{phys}}=0.175$ with $m_s^{\mathrm{phys}}$ being the physical strange quark mass in real-life QCD. The critical pion mass in the three-flavor symmetric limit, on the second-order boundary, is measured at $m_{\pi }\sim 52.4\mathrm{MeV}$, with the critical temperature $T_c\sim 51.7\mathrm{MeV}$.

The production of a pair of on-shell $Z$-bosons is an important process at the LHC. Owing to its large production cross section at the LHC, this process is very useful for Standard Model precision studies, electroweak symmetry breaking sector as well as to unravel the possible new physics. In this work, we have performed the threshold resummation of the large logarithms that arise in the partonic threshold limit $z\to 1$, up to next-to-next-to-leading logarithmic (NNLL) accuracy. The presence of the two-loop contributions in the process-dependent resummation coefficient $g_0$ makes the numerical computation a nontrivial task. After matching the resummed predictions to the next-to-next-to-leading order (NNLO) fixed-order results, we present the invariant mass distribution to $\mathrm{NNLO}+\mathrm{NNLL}$ accuracy in QCD for the current LHC energies. We find that in the high invariant mass region ($Q=1\mathrm{TeV}$), while the NNLO corrections are as large as 83% with respect to the leading order, the NNLL contribution enhances the cross section by additional few percent, about 4% for 13.6 TeV LHC. In this invariant mass region, the conventional scale uncertainties in the fixed-order results get reduced from 3.4% at NNLO to about 2.6% at $\mathrm{NNLO}+\mathrm{NNLL}$, and this reduction is expected to be more for higher $Q$ values.

A recent independent dark photon (DP) focused reanalysis of existing data from the TASEH axion haloscope experiment reported a tentative DP dark matter signal with local significance $\sim 4.7\sigma$ at a frequency $f\approx 4.71\mathrm{GHz}$, corresponding to $m_X\approx 19.5\mathrm{\mu }\mathrm{eV}$ and kinetic mixing $ϵ\sim 6.5\times {10}^{-15}$. Motivated by this report, we performed a dedicated, narrowband follow-up experiment to confirm or refute the signal with a cryogenic microwave cavity operated without a magnetic field, leveraging the ORGAN-Q dilution refrigeration and receiver chain. Scanning a window centered on the reported frequency over a live time of $T_{\mathrm{int}}\sim 13\mathrm{days}$, we find no excess consistent with a dark photon signal as reported, and set a 95% CL of $ϵ\le 5.04\times {10}^{-15}$ in a narrow mass range around $\sim 19.5\mathrm{\mu }\mathrm{eV}$, excluding a signal of the strength and frequency reported to 99.92% confidence. We discuss the experiment and present the exclusion limits.

We discuss the first implementation of the Martini-Ericson-Chanfray-Marteau random phase approximation-based (anti)neutrino cross-section model for quasielastic (1p1h) and multinucleon (2p2h and 3p3h) excitations in the widely used GENIE neutrino event generator. Validation steps are presented, in particular, through direct comparisons of GENIE cross-section output with original calculations performed by the authors of the model. Predictions for ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{40}\mathrm{Ar}$ are compared with some available T2K and MicroBooNE experimental measurements showing a reasonable agreement.

Driven by the increasing volume of recorded data, the demand for simulation from experiments based at the Large Hadron Collider will rise sharply in the coming years. Addressing this demand solely with existing computationally intensive workflows is not feasible. This paper introduces a new fast simulation tool designed to address this demand at the LHCb experiment. This tool emulates the detector response to arbitrary multibody decay topologies at the LHCb. Rather than memorizing specific decay channels, the model learns generalizable patterns within the response, allowing it to interpolate to channels not present in the training data. Novel heterogeneous graph neural network architectures are employed that are designed to embed the physical characteristics of the task directly into the network structure. We demonstrate the performance of the tool across a range of decay topologies, showing that the networks can correctly model the relationships between complex variables. The architectures and methods presented are generic and could readily be adapted to emulate workflows at other simulation-intensive particle physics experiments.

On a spherically symmetric and static background, we study the existence of linearly stable black hole (BH) solutions in nonlinear electrodynamics (NED) with a Horndeski vector-tensor (HVT) coupling, with and without curvature singularities at the center ($r=0$). Incorporating the electric charge $q_E$ and the magnetic charge $q_M$, we first show that nonsingular BHs can exist only if $q_M=0$. We then study the stability of purely electric BHs by analyzing the behavior of perturbations in the metric and the vector field. Nonsingular electric BHs are unstable due to a Laplacian instability in the vector perturbation near the regular center. In the absence of the HVT coupling ($\beta =0$), singular BHs in power-law NED theories can be consistent with all linear stability conditions, while Born-Infeld BHs encounter strong coupling due to a vanishing propagation speed as $r\to 0$. In power-law NED and Born-Infeld theories with $\beta \ne 0$, the electric fields for singular BHs are regular near $r=0$, while the metric functions behave as $\propto r^{-1}$. Nevertheless, we show that Laplacian instabilities occur for regions inside the outer horizon $r_h$, unless the HVT coupling constant $\beta$ is significantly smaller than $r_h^2$. For $\beta \ne 0$, we also reconstruct the NED Lagrangian so that one of the metric functions takes the Reissner-Nordström form. In this case, there exists a branch where all squared propagation speeds are positive, but the ghost and strong coupling problems are present around the BH center. Thus, the dominance of the HVT coupling generally leads to BH instability in the high-curvature regime.

We investigate the advantage of using squeezed input light for generating gravity-induced entanglement (GIE) through Fourier-domain analysis. Based on the findings of Miki et al. [Phys. Rev. D 109, 064090 (2024).], which demonstrated the feasibility of detecting GIE in optomechanical systems under quantum control, we further demonstrate that squeezed input light can reduce the optical noise in the mechanical conditional state and enhance GIE. Furthermore, we estimate the systematic and statistical errors in the measurement of GIE using the Fourier transformation over a finite measurement time. Based on the error estimations using the signal-to-noise ratio in GIE detection, we find that a total measurement time of ${10}^6\mathrm{s}$ is required to achieve $\mathrm{SNR}=1$ when using squeezed input light, whereas ${10}^{6.8}\mathrm{s}$ is needed without squeezed input light. This result highlights the effectiveness of optomechanical systems and the critical role of squeezed input light in enhancing the detectability of GIE.

In this article, we extend our previously presented analytical formulas [J. Claros and E. Gallo, [Phys. Rev. D 109, 124055 (2024)] ] for describing light rays passing near or emitted in the vicinity of compact objects to a broader class of spherically symmetric, static spacetimes, including the Johansen–Psaltis and Rezzolla-Zhidenko metric families. The generalized formulas retain the simplicity and accuracy of the original approach while allowing for more general deviations from Schwarzschild geometry. These expressions provide an approximate yet accurate mapping between emission points and the image plane of an asymptotic observer, enabling fast analytical computations of accretion disk images, polarization of the emitted radiation, luminosity curves associated with pulsars, and other related applications. As examples, we compute isoradial curves for several metric families and the Stokes parameters $Q$ and $U$ for a hot spot orbiting near a black hole described by one of the studied metrics, presenting the corresponding polarization ($QU$) curves.

We quantify the impact of strong magnetic fields (assuming $B=B_0·r_0^3/r^3$ with $B_0\gtrsim {10}^{16}\mathrm{G}$) on the neutrino transport in core-collapse supernovae (CCSNe). Magnetic fields quantize the momenta of electrons and positrons, resulting in an enhanced absorption cross section for low-energy neutrinos and suppressed chemical potentials for $e^{\pm }$. We include these changes in the M1 scheme for neutrino transport and perform 1D CCSNe simulations with gr1d. The increased low-energy cross sections reduce the ${\overline{\nu }}_e$ mean energy $⟨E_{{\overline{\nu }}_e}⟩$ while elevating the neutrino number luminosities ${\mathcal{L}}_{\nu }$ for both ${\nu }_e$ and ${\overline{\nu }}_e$ due to the lower-energy weighted spectra. The reduction of chemical potential enhances the ${\overline{\nu }}_e$ emission while suppressing that of ${\nu }_e$, thereby driving an increase in the electron fraction behind the stalled shock at $\sim 30–100\mathrm{km}$. This further amplifies $⟨E_{{\nu }_e}⟩$ through an increased electron density. Consequently, magnetic fields amplify $L_{{\nu }_e}$ by increasing both ${\mathcal{L}}_{{\nu }_e}$ and $⟨E_{{\nu }_e}⟩$, whereas for ${\overline{\nu }}_e$, the rise in ${\mathcal{L}}_{{\overline{\nu }}_e}$ is offset by a decreased $⟨E_{{\overline{\nu }}_e}⟩$, leading to a minimal change in $L_{{\overline{\nu }}_e}$. A systematic parameter scan of dipole field configurations suggests that, for $r_0>30\mathrm{km}$, $⟨E_{{\overline{\nu }}_e}⟩$ is significantly suppressed and $L_{{\nu }_e}$ is enhanced if $B_0\ge 2.7\times {10}^{16}\mathrm{G}$. These magnetic effects become negligible for $B_0$ below $\sim 7.4\times {10}^{15}\mathrm{G}$.

We explore the possibility of phase transitions between different quark matter phases occurring within quark stars, giving rise to the hybrid quark stars (HybQSs). First, we obtain the generic phase diagram of possible mass-radius relation forms for the HybQSs. Then, utilizing a well-established general parametrization of interacting quark matter, we construct quark star models featuring sharp first-order quark-quark phase transitions of various types, in contrast to the hadron-quark transition in conventional hybrid stars. We systematically investigate how recent observations, such as the pulsar mass measurement $M_{\mathrm{TOV}}\gtrsim 2M_{\odot }$ and the GW170817’s tidal deformability bound ${\mathrm{\Lambda }}_{1.4M_{\odot }}<800$, constrain the viable parameter space. We also identified twin stars in some of the HybQS parameter space. Furthermore, we found that the quark-quark phase transitions in hybrid quark stars may also cause the deviation from the approximate universal relation between the dominant postmerger frequency $f_{\mathrm{peak}}$ and tidal deformability ${\mathrm{\Lambda }}_{1.35M_{\odot }}$, which was previously believed to only be caused by the hadron-quark phase transitions in hybrid neutron stars. This work unveils new possibilities of phase transitions and the resulting new types of compact stars in realistic astrophysical scenarios.

SS 433 is one of the most extreme Galactic x-ray binaries, launching semirelativistic jets and showing clear signs of super-critical accretion onto what is likely a black hole. Yet the properties of the binary system that produced it remain uncertain. To solve the inverse problem of inferring the progenitor properties of binaries that evolve into SS 433-like systems, we use an iterative, simulation-based calibration framework that combines Bayesian inference with the isolated binary-evolution code COSMIC. Using six measured properties of SS 433 and the dynamic nested sampler dynesty, we explore a ten-dimensional space of possible progenitor masses, orbits, mass-transfer histories, and natal-kick velocities. This approach identifies the regions of parameter space most consistent with SS 433 and allows us to iteratively refine the resulting progenitor distributions. We find 90% confidence intervals for the progenitor initial primary mass of $(8,11),M_{\odot }$, secondary mass of $(32,40),M_{\odot }$, orbital period of (136, 2259) days, eccentricity of (0.26, 0.6), common-envelope efficiency of (0.44, 0.76), accreted fraction during stable mass transfer of (0.22, 0.6), and black-hole natal-kick magnitude of (5, 68) km/s. These results show that direct probabilistic inference of x-ray binary progenitors can yield new constraints on the formation of extreme accretion systems like SS 433, which has important implications for theoretical expectations of the population of SS 433-like systems in the Galaxy and their connection with cosmic ray observations.